Ocean acidity rising faster than feared

Ocean acidification, pronounced earlier on this blog as “the next big climate thing,” may be even bigger.

Australian researchers are arguing that their evidence shows the oceans are growing more acid faster than expected, and that the consequences could be on par with those of worldwide warming.

“Recent research into corals using boron isotopes indicates the ocean has become about one third of a pH unit more acid over the past fifty years. This is still early days for the research, and the trend is not uniform, but it certainly looks as if marine acidity is building up,” says Professor Malcolm McCulloch of the ARC Center of Excellence for Coral Reef Studies (CoECRS) and the Australian National University.

That sounds conservative, but McCulloch goes on to say: “It appears this acidification is now taking place over decades, rather than centuries as originally predicted. It is happening even faster in the cooler waters of the Southern Ocean than in the tropics. It is starting to look like a very serious issue.”

Australian researchers will review the latest science at the Coral Reef Futures 07 Forum this weekend (Oct. 19-20) in Canberra.

To summarize, there's a great deal more carbon dioxide in the atmosphere than there was a century ago, and the amount is continuing to increase as humans burn fossil fuels and forests. That CO2 mixes with water in the oceans to form carbonic acid, and slowly, the seas become more acidic.

That's a problem because a lot of the sea's creatures, including corals, shells and other things, have chalk skeletons that dissolve in the presence of acid, or at least form less readily in a more acid environment. Among things affected are certain plankton, which are a fundamental part of the oceanic food web—the stuff that tuna, whales and the other big creatures ultimately depend on.

“Analysis of coral cores shows a steady drop in calcification over the last 20 years. There’s not much debate about how it happens: put more CO2 into the air above and it dissolves into the oceans,” said Professor Ove Hoegh-Guldberg of CoECRS and the University of Queensland.

Hoegh-Guldberg did experiments in aquariums containing corals. When he increased CO2 levels in the air above the aquarium water, the corals stopped forming their skeletons, which are the source of reefs.

He also found that the rock-forming algae—coralline algae or red calcareous algae—that are another key reef builder, began to dissolve at high CO2 levels.

The oceans are still some time from that, but atmospheric CO2 has gone up from 305 to 385 parts per million from 1960 to now. If they reach 500 parts per million, “you put calcification out of business in the oceans,” Hoegh-Guldberg said.
“As an issue it’s a bit of a sleeper. Global warming is incredibly serious, but ocean acidification could be even more so.”

© 2007 Jan W. TenBruggencate

For information about the Australian forum, see:
http://www.coralcoe.org.au/news_stories/07/forum_program.html